Jul 29, 2011 16:50 GMT  ·  By

Twitter has begun public field tests for a new ad delivery system that involves inserting paid tweets from followed organizations at the top of people's timelines.

Called promoted tweets these messages will behave just like any other messages do once displayed. This means they will scroll normally, will appear only once and will be removable.

What sets them appart is when they're displayed. Promoted tweets will appear when users log in or refresh their timelines.

Tweets are normally displayed in the order they were posted by their authors and if someone doesn't refresh their timeline for an hour, when they finally do, they might never scroll down to see all the messages they missed.

By promoting their tweets companies can make sure that more followers will see them because they will also reach those who were offline at the time when the messages were posted.

However, promoting a tweet successfully is not as simple as paying a certain amount of money. Twitter decides what tweet to promote to a particular user at a certain time based on both relevance and pricing.   Companies will bid for their chance to get promoted, but they will only pay if the users actually engage with their tweets. Actions that are considered engagement include clicking, retweeting, marking as a favorite or replying.

Twitter claims that this new ad system is also beneficial to users because it prevents them from missing important offers or announcements from the organizations they follow. "We’ll be rolling out and testing this new offering over the next several weeks with a select group of partners," the company announces on its official blog.

These partners include companies like Best Western, Dell, Gatorade, Groupon, HBO, JetBlue, LivingSocial, Microsoft Xbox, Red Bull, Sephora, Starbucks, Summit Entertainment’s “50/50”, TNT and Virgin America, but also non-profit organizations like charity: water, Make-A-Wish Foundation, Room to Read, The American Red Cross and Water.org.